Once the skin has a wound, a huge amount of exudation is generated, which is called the ‘inflammatory phase’, then the proliferative phase occurs, in which granulation takes place, and finally the growing phase occurs in which newly generated skin becomes firm as the wound heals. The most important factor in the process of wound healing is to minimize the inflammatory phase by quickly absorbing exudation generated in the early inflammatory phase and to maintain proper moisturizing conditions during the growing phase to provide various cell growth factors (PDGF, TGF-β, EGF, FGF, VEGF, IGF, etc) or cytokines (IL-1, IL-6, IL-8, TNF, etc) to accelerate wound healing by helping cell migration and proliferation. It is preferable to use a dressing material that does not adhere to the wound.
The conventional gauze dressing absorbs wound exudate easily, but at the same time has the disadvantages of not-defending itself against infection by bacteria, keeping the wound area dry which delays recovery, and difficulty in changing dressings because it adheres to the wound, possibly damaging nascent tissues and causing pain. In the early treatment phase, a lot of exudate is generated so the dressing has to be changed frequently (for example, several times a day). As an alternative to overcome the disadvantages of the conventional gauze dressing, various obstructive dressing materials have been developed, but these new dressings are expensive, lack adequate absorption, and cannot regulate their water vapor permeability. Thus, the obstructive dressing materials are only applied to some specific types of wounds.
The obstructive dressing materials in use are films, hydrocolloids, hydrogels, polyurethane foams, etc. Particularly, hydrocolloids, hydrogels and polyurethane foams are favored because of their high treatment effect.
U.S. Pat. No. 5,503,847 and No. 5,830,932 describe a hydrocolloid dressing material which is composed of an adhesive composition layer, a hydrocolloid layer that absorbs impact and exudation, and a film layer that prevents the invasion of bacteria and impurities.
The hydrocolloid dressing material absorbs a small amount of wound exudate to form a gel and is able to provide humid conditions and maintain the pH as weakly acidic for a long time to prevent the disturbance of tissues and promote cell growth. However, water vapor permeability and exudation absorption are not satisfactory. During the change or removal of the dressing, the gel adheres to the wounded area and remains there, requiring secondary treatment to eliminate the residue. Thus, this dressing is not suitable for application to a wounded area that generates a large amount of exudate.
U.S. Pat. No. 5,501,661 and No. 5,489,262 describe a hydrogel dressing material. According to these descriptions, the hydrogel dressing material contains a non-permeable polymer film coated with hydrogel. The polymer film prevents dehydration or dryness of the hydrogel, and the hydrogel layer absorbs exudation by adhering to a wounded area and maintains humid conditions to accelerate wound healing. However, this dressing material is not suitable for application to a severe wound that generates a lot of exudation because of its low water vapor permeability and water absorptiveness. Excessive absorption of the dressing material deforms the dressing material itself, thereby making it difficult to change the dressing, and causes infection of normal tissues.
U.S. Pat. No. 5,445,604 and No. 5,065,752 describe a hydrophilic polyurethane foam dressing material having a triple layer structure in which both sides of the polyurethane foam are laminated with a film. Particularly, a wound contact layer film, which is laminated to prevent the huge wound contact layer pores from adhering to the wounded area, is designed to have a hole through which exudation is absorbed into the wound contact layer. However, exudation and blood cannot be completely absorbed from the wounded area, which generates blood clots on the area. Because of the generated blood clots, wound healing is retarded or the dressing adheres to the wound, and nascent tissues might also adhere to the dressing through the huge mechanically made pores, making it difficult to change the dressing and resulting in a dot shaped scar. When this dressing material is applied to a wound generating lots of exudation, the dressing has to be changed frequently because of the insufficient absorptiveness per unit area and the patient's clothes or sheets have to be changed often because exudation flows out through the dressing due to external forces owing to its weak moisturizing rate. In addition, the dryness around the wound or dryness of the wounded area itself when applied on a wound generating less exudation is another problem of this dressing material (J Korean Soc. Plast. Reconstr. Sur., Vol. 29, No. 4, 297-301, 2002; J Korean Burn Soc., Vol. 6, No. 1, 45-51, 2003).
U.S. Pat. No. 5,064,653 and No. 5,254,301 also describe a hydrophilic polyurethane foam dressing material. According to these descriptions, the dressing material has a triple layer structure in which a polyurethane foam produced by in situ reaction of a hydrophilic isocyanate-capped polyether prepolymer with a hydrotrope, water, an adjuvant and a wetting agent is laminated with films by two-part adhesive, which used to be added during continuous line foaming. Hydrophilicity and moisturizing rate have been improved by applying a hydrotrope and a wetting agent on the wound contact layer. However, the dressing material is still not suitable for operation wounds which produce a lot of exudation including blood, because excessive exudation is not absorbed in the dressing material and flows out through the wound contact layer to the patient's clothes or a sheet. In addition, the remaining blood generates blood clots on the wounded area, retarding wound healing, and the pore of the wound contact layer is bigger than a human cell so re-generated tissues adhere to the dressing, making it difficult to change the dressing (J Korean Burn Soc., Vol. 6, No. 1, 45-51, 2003).
The alternative to overcome the above mentioned problems has been proposed by the present inventors and described in Korean Patent No. 553078. According to the description, the polyurethane foam dressing material having a double-layer structure, in which an absorption layer having a water absorptiveness of 400˜2,000 weight % is laminated with a protective film having a water vapor permeability of 200˜1,500 g/m2·day, is a ground-breaking development in wound healing. However, it still has a problem with regard to dryness around the wounded area when it is applied on a wound generating less exudation. Thus, a novel dressing material needs to be developed with an improved moisturizing rate that enables a hydrogel-like effect after absorbing exudation to provide comfortable humid conditions.